This invention relates generally to a printing circuit technique, and more particularly to a method for producing electric and electronic printed circuits on an insulating substrate or insulating board.
Heretofore, for instance an electric resistor, which is an important component in a printed circuit, has been produced on an insulating board made of, for instance, a phenolic resin having a fabric reinforcement by firstly printing thereon an electric resistance layer of a shape corresponding to the resistor, and then applying an electrically conductive layer adapted to form terminals of the resistor in such a manner that these two layers are superposed on each other at both end portions of the resistance layer.
The application of the electrically conductive layer to form terminals of the resistor on the insulating substrate or board has been carried out by applying an electrically conductive paste including metal particles, such as silver particles, thereon and then drying it out to be solidified. However, there has been a tendency for the metal particles directly contacting the insulating substrate to migrate in the direction of an electric field applied thereto and along the reinforcing fabric contained in the insulating substrate. Consequently the insulation between the conductive layer portions forming the terminals of the resistor tends to be deteriorated during long period of operation until a short-circuit occurs between these portions so that the function of the resistor is substantially lost.
In order to eliminate the above described disadvantage of the prior art, a suitable resin layer has been applied on a required area of the insulating substrate, and the resistance layer and the electrically conductive layer have been applied over the resin formed layer so that the migration of the metallic particles is thereby substantially prevented. However, such a procedure has required an additional step of forming the resin layer, thus requiring additional labor and time, and this fact constitutes a drawback of the conventional practice.